Characteristics of atmospheric aerosols and their radiative impacts show large variations in space and time, leading to
large uncertainties in the climate impact assessment. Despite the concerted efforts in the last decade through several
field campaigns, the uncertainty still persists. This essentially arises due to lack of a comprehensive data on several
aerosol parameters with adequate spatial resolution and for long duration. This is particularly true for the Indian region,
with large geographical diversities, large density of population, diverse living habits and rapid industrialization. With a
view to addressing to this problem and to evolve a regional scale database for assessing the radiative impacts of
aerosols, an integrated, multi-platform field campaign, ICARB, was carried out during March-May 2006, under the
ISRO's Geosphere Biosphere Programme. The campaign involved participation by more than 100 scientists from about
35 different institutions across the country and collocated observation over the mainland, over oceans and same time
measurements of altitude profiles using aircrafts. A campaign of this magnitude is carried out for the first time in this
region, and perhaps for the first time globally. The mainland observations included a network of aerosol observatories
over Indian landmass and from islands in the Arabian Sea and Bay of Bengal, while a dedicated scientific cruise of 64-
days duration covered the vast oceanic regions around India. Altitude profiles were obtained using research aircraft of
the National Remote Sensing Agency, from 5 different bases. The details of the campaign and the preliminary findings
will be presented.
Enhanced aerosol loading over the Indo-Gangetic Plain (IGP) is a regular feature during winter months. In addition to the environmental degradation and reduced visibility, these aerosols can cause significant radiative impact also. In view of this, a campaign mode observation under ISRO-GBP was conducted in December 2004 to characterize the aerosol properties over the IGP. As part of this, extensive measurements of aerosol BC were made from Kharagpur, an inland rural location lying at the eastern end of the Indo Gangetic Plain. It also lies close to several industrialized regions and area having lot of mining activities
Results showed, extremely high BC concentration, often exceeding ~20 mg m-2, prevailed during December. During this period, BC concentration also showed large diurnal variation. Simultaneous measurements of the local atmospheric boundary layer height and wind fields revealed a very close association between the BC concentration and the ventilation coefficient (defined as the product of the boundary layer height and the transport wind). Back trajectory analyses using HYSPLIT revealed that in addition to the local boundary layer dynamics, the changes in the advection pathways also influence the concentration of BC.
In this paper, we report the results of extensive, and all-season, collocated, measurements of several aerosol parameters
[such as spectral aerosol optical depth (AOD) at 10 bands spanning from UV to IR; mass size distribution and mass
concentration of composite aerosols; as well as mass concentration and mass mixing ratio of aerosol black carbon (BC)]
for over a 4-year period (January 2000 to December 2003), from an unindustrialized coastal location, Trivandrum
(8.55°N, 76.9°E), close to the southern tip of Indian peninsula and use these properties to estimate the aerosol short wave
radiative forcing. The results show that the top of the atmosphere (TOA) forcing is significantly positive during winter
while it changes to negative during monsoon and post monsoon seasons. The surface forcing decreases from winter to
summer. Consequently, the net atmospheric absorption decreases from a high value in winter to low values during
monsoon.
Continuous and near-real-time measurements of BC were made for a period of two years from the I-LARC (ISRO Laboratory for Aerosol Radiation and Chemistry) station in Port Blair as a part of the ISRO Geosphere Biosphere Programme (I-GBP). These are used to characterize BC, for the first time over the Bay of Bengal (BoB), which is surrounded by distinct landmasses having highly varying anthropogenic activities. Significantly high concentrations (~2.4 μg m-3) occur during the period September to April. During this period, BC contributes ~ 6.5 % to the composite aerosol mass concentration. The concentration and its share to the composite aerosols decrease rapidly (by a factor of >3) and remain so during the period June to August when the station is under the influence of monsoon winds coming from the Indian Ocean. Back-trajectory analyses reveal five potential advection pathways, which are seasonal in nature and have a strong influence on the BC concentrations over the island. The results and their implications will be discussed.
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